This invention relates to a process for the preparation of acyloxyphthalic anhydrides and oxydiphthalic anhydride from halophthalic anhydrides. More particularly, this invention relates to the use of benzoic acids, substituted benzoic acids, benzoic acid salts, substituted benzoic acid salts, benzoyloxyphthalic anhydrides, and substituted benzoyloxyphthalic anhydrides as catalysts for the reactions of a halophthalic anhydride to yield the compounds noted above.
Acyloxyphthalic anhydrides are particularly useful in the synthesis of oxydiphthalic anhydrides. By known methods the acyloxyphthalic anhydrides can be hydrolyzed to yield hydroxyphthalic anhydrides. The hydroxyphthalic anhydrides can be used to prepare oxydiphthalic anhydrides (U.S. Pat. No. 4,837,404). The acyloxyphthalic anhydrides are also useful as curing agents for epoxy resins. The other product of this invention, oxydiphthalic anhydride, is useful as a monomer for the preparation of polyimide resins. Polyimides can be produced by reacting an oxydiphthalic anhydride with a suitable diamine and dehydrating the resulting polyamic acid. Polyimide resins are particularly useful in electrical and high temperature applications.
Oxydiphthalic anhydride has been prepared by several methods. U.S. Pat. No. 4,697,023, incorporated herein by reference, discloses that a halophthalic anhydride, water, and an alkali metal compound such as potassium fluoride or potassium carbonate will react, in the presence of a dipolar aprotic solvent, to form oxydiphthalic anhydride.
U.S. Pat. No. 4,837,404 teaches that oxydiphthalic anhydride can be prepared by reacting a halophthalic anhydride with an hydroxyphthalic anhydride in a polar aprotic solvent in the presence of an alkali metal compound such KF, CsF, or K.sub.2 CO.sub.3.
U.S. Pat. No. 4,808,731 teaches a method of preparing oxydiphthalic anhydride by reacting a substituted phthalic anhydride such as 4-nitro or 4-fluorophthalic anhydride with a dialkyl aminopyridine in the presence of a refluxing, non-polar organic solvent.
U.S. Pat. No. 4,558,164 discloses a process for preparing a symmetrical dinitrodiphenyl ether from o- or p-nitrochlorobenzene or o- or p-nitrofluorobenzene comprising using a polar organic solvent, a potassium salt of a fatty carboxylic acid containing 2 to 20 carbon atoms or a potassium salt of an aromatic carboxylic acid containing 7 to 12 carbon atoms as catalyst, and either sodium or potassium carbonate to react with the p-nitrochlorobenzene. The reaction is carried out at from 150.degree. to 210.degree. C. until the o- or p-nitrochlorobenzene or o- or p-nitrofluorobenzene reacts. The method of U.S. Pat. No. 4,558,164 (Example 5) was tested using 4-chlorophthalic anhydride as a starting material. No oxydiphthalic anhydride was produced. (see Comparative Examples 3 and 4)
U.S. Pat. No. 4,780,544 teaches a method of preparing oxy-di(N-alkyl or aryl) phthalimides. In this process nitro-N-alkyl or aryl phthalimide is treated with an alkali metal carboxylate salt. Sodium, potassium, and cesium salts of acetic acid, propionic acid and benzoic acid are disclosed as suitable carboxylate salts and the effective amount is 0.25 to 1 mole of carboxylate per mole of nitrophthalimide.
Muehlemann (Pharm. Acta Helv. 23; 1948 p. 257) discloses the preparation 3-acetoxyphthalic acid from 3-hydroxyphthalic acid and acetic anhydride. Similarly, Japanese Patent application 85-238,404 as abstracted in CA 107 (22):199080 g, discloses that 4-hydroxyphthalic anhydride biesters can be prepared by the condensation of 4-hydroxyphthalic anhydride with diacid chlorides. The biesters are formed from the di-acid chloride and the hydroxy portion of the hydroxyphthalic anhydride. The anhydride portion of the molecule remains intact. German Patent DE1901028 (August, 1970), discloses that terephthalate esters of hydroxyphthalic anhydride can be prepared by the transesterification of 4-acetoxyphthalic anhydride with terephthalic acid in the presence of magnesium.